Browsing by Subject "DMA"
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Item Application of surface energy measurements to evaluate moisture susceptibility of asphalt and aggregates(Texas A&M University, 2005-08-29) Zollinger, Corey JamesMoisture damage in asphalt mixes can be defined as loss of strength and durability due to the presence of moisture at the binder-aggregate interface (adhesive failure) or within the binder (cohesive failure). This research focuses on the evaluation of the susceptibility of aggregates and asphalts to moisture damage through understanding the micro-mechanisms that influence the adhesive bond between aggregates and asphalt and the cohesive strength and durability of the binder. Moisture damage susceptibility is assessed using surface energy measurements and dynamic mechanical analysis (DMA). Surface energy is defined as the energy needed to create a new unit surface area of material in vacuum condition. Surface energy measurements are used to compute the adhesive bond strength between the aggregates and asphalt and cohesive bond strength in the binder. DMA testing is used to evaluate the rate of damage accumulation in asphalt binders and mastics. The DMA applies a cyclic, torsional strain controlled loading to cylindrical asphalt mastics until failure. The DMA results are analyzed using continuum damage mechanics that focuses on separating the energy expended in damaging the material from that associated with viscoelastic deformation. A new approach is developed to analyze the DMA results and calculate the rate of damage. The developed approach is used to evaluate six asphalt mixtures which have performed either well or poorly in the field. The resistance of the field mixes to moisture damage is shown to be related to the calculations of bind energies and the accumulated damage in the DMA.Item Methyl arsenic adsorption and desorption behavior on iron oxides(Texas A&M University, 2005-08-29) Lafferty, Brandon JamesArsenic is a toxic element that is widely distributed throughout the earth??s crust as a result of both natural geologic processes and anthropogenic activities. In virtually all environments, methylated forms of arsenic can be found. Because of the widespread distribution and toxicity of arsenic and methyl-arsenic, their adsorption behavior on soil minerals is of great interest. Although considerable attention has been given to the behavior of inorganic arsenic on mineral surfaces, little research has been conducted regarding interactions of the methyl-arsenic forms. The objective of this study was to compare the adsorption and desorption behavior of methylarsonate (MMAsV), methylarsonous acid (MMAsIII), dimethylarsinate (DMAsV), dimethylarsinous acid (DMAsIII), arsenate (iAsV), and arsenite (iAsIII) on iron oxide minerals (goethite and ferrihydrite) by means of adsorption isotherms and adsorption envelopes. Additionally, desorption envelopes were obtained using sulfate and phosphate as competitive ligands. Arsenic was measured by FI-HG-AAS. MMAsV and iAsV were adsorbed in higher amounts than DMAsV on goethite and ferrihydrite at all pH values studied. Although MMAsV and iAsV were adsorbed quantitatively at lower concentrations on goethite and ferrihydrite, as arsenic concentration was increased MMAsV was adsorbed in slightly lower quantities than iAsV. DMAsV was not quantitatively adsorbed at any concentration on goethite or ferrihydrite. MMAsV and iAsV exhibited high adsorption affinities on both goethite and ferrihydrite at pH values below 9 and showed decreasing adsorption above this point (more rapidly for MMAsV). DMAsV was adsorbed only at pH values below 8 on ferrihydrite and below 7 on goethite. MMAsV, iAsV, and DMAsV each exhibited adsorption characteristics suggesting specific adsorption on both goethite and ferrihydrite. Increased methyl substitution resulted in increased ease of arsenic release from the iron oxide surface. MMAsIII and DMAsIII exhibited no evidence for any type of specific adsorption under the conditions studied. Phosphate was a more effective desorbing ion than sulfate, but neither desorbed all arsenic species quantitatively.